The present invention pertains to a process operating an electrochemical measuring cell, which is connected to a potential voltage source with a pulse generator to generate potential voltage pulses and to which at least one potential voltage U0 supplied by the potential voltage source is applied in the measuring operation.
A process for automatically checking the characteristics of an electrochemical gas-measuring cell, in which different voltage pulse trains are applied to the gas-measuring cell which is in the measuring operation, has been known from DE 38 09 107 C1. Changes in the sensitivity of the gas-measuring cell can be inferred from a comparison of the impressed voltage pulses with the corresponding current pulses. Thus, it can be determined, e.g., during the measuring operation whether the sensitivity has changed briefly or over the long term.
A process for improving the break-in characteristic of electrochemical measuring cells has been known from DE 44 45 948 C2; this process is based on setting the potential voltage at an increased value after switching on for a predetermined length of time so that the sensor current resulting from the increased potential voltage will come close to the stationary sensor rest current after a short time.
The prior-art process has the drawback that measurement cannot be begun immediately after switching on the electrochemical measuring cell, because stationary operating conditions must first be established. In addition, the break-in time of an electrochemical measuring cell depends on the concentration of the gas to be detected in the environment of the measuring cell. If, e.g., the measuring cell is exposed to the gas to be detected without potential voltage applied, an electrochemical reaction, which leads to a change in potential at the electrodes, takes place within the measuring cell because of diffusion processes. This potential shift must first be eliminated after switching on.
The primary object of the present invention is to provide a process and system for operating an electrochemical measuring cell, with which it is possible to carry out gas concentration measurements just a short time after switching on the operating potential voltage.
According to the invention a process for operating an electrochemical measuring cell is provided as well as a system and device for accomplishing the process. The measuring cell is connected to a potential voltage source with a pulse generator to generate potential voltage pulses and to which at least one potential voltage U0 supplied by the potential voltage source is applied in the measuring operation. The potential voltage pulses are applied in steps to the said measuring cell in a state of readiness of the said measuring cell, in which the potential voltage U0 is switched off.
It has been surprisingly found that an electrochemical measuring cell, to which potential voltage pulses are applied at regular intervals in the state of readiness, in which the potential voltage is switched off, can be used for measuring purposes almost without delay after the potential voltage necessary for the measuring operation has been applied. The pulsed operation during the state of readiness is especially significant for portable, battery-operated measuring instruments, because the readiness to operate can thus be maintained for a long time without excessive power consumption. Only about 4% of the power needed during the measuring operation is needed in the state of readiness compared with the measuring operation with constant potential voltage applied.
It is especially advantageous for the potential voltage pulses to have the amplitude of the potential voltage occurring during operation. Readiness of the measuring cell to operate can thus be achieved in an especially short time after switching on the potential voltage.
The potential voltage pulses are selected to be such that the duration of the interpulse period is between 1 minute and 60 minutes.
Preferred values for the pulse length are between 8 sec and 30 sec.
It is advantageous to select the ratio of the pulse length to the duration of the interpulse period between 1:10 and 1:100.
The ratio of the pulse length to the duration of the interpulse period to be set depends on the concentration of the gas component to be detected, which occurs during the state of readiness. Since correspondingly more gas molecules enter the interior of the measuring cell due to diffusion processes at a high gas concentration, a correspondingly high ratio of the pulse length to the duration of the interpulse period shall be set, i.e., a value in the direction of 1:10.
It is especially advantageous for the ratio of the pulse length to the duration of the interpulse period during the state of readiness to be adjusted to the gas concentration by performing gas concentration measurements at predetermined intervals in the course of the state of the readiness and by setting the ratio of the pulse length to the duration of the interpulse period corresponding to the gas concentration measured.
Exemplary embodiments of the present invention are shown in the drawings and will be explained in greater detail below.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.